Saline variability at the south-west of Portugal after kriging data from Ramalina spp. biomonitors

Sea-salt input over the land masses may have deleterious effects on man-made structures, vegetable organisms (crops and vegetation) and soil/water resources. Recent work has shown the ability of some lichen species to monitor the deposition of airborne salts of marine origin. The atmospheric transport and deposition of sea salts can be assessed by measuring saline elements in lichens growing over coastal areas. The concentration of Cl- and Na+ was determined in lichen thalli collected in three different dates on the south-west region of Portugal. The extracellular fraction of Na+ was obtained by a sequential elution procedure, and Cl- was determined after leaching samples with water. The dispersion of element grades in the area was studied through geostatistical analysis. Numerical values were estimated by two interpolation methods: ordinary kriging and kriging with an external drift. The latter method used the logarithm of the distance to the coast as an auxiliary variable and yielded more reliable results. Every set of data produced a similar spatial pattern, showing a steep gradient in the first three kilometres from the coast. However, considerable variation can be observed between surveys. The variability of results is interpreted using the precipitation data obtained for the region under consideration. (author)